In our current world of Fashion it is usual to call it a "Suit" if a Jacket and trousers are of the same fabric and designed to be worn together.

But fashion has always had room for wearing a Jacket that does not match the trousers.

This not only applies to color and pattern. A Tweed Wool Jacket paired with Cotton Cord trousers has been a very nice look for quite a while now.

The same goes with Wool and Linen. A pair of light "Tropical" Wool trousers paired with a Linen Coat has been worn, and in style, since the British started to hang out at the Raffles Hotel.

The "Rules" only come into effect as far as fashion is concerned when it comes to the pairing of some patterns and some color combinations.
You don't usually wear trousers with a Horizontal pattern with a Jacket that has a Vertical pattern.

You don't usually wear a Blue Jacket with Brown trousers. Not that it can't be done and sometimes is but in very general terms Blue colors go with Grays, & Blacks while Browns go with Reds and Greens.

But then again, no hard and fast rules.

This whole matching thing is overrated in my opinion. While it is common to try to pull a color out of the Kilt to match the hose, flashes or shirt with It is also common to use the Kilt as a stand alone while matching the other parts of the outfit to each other regardless of the color of the Tartan in the Kilt.

The bad part of allowing everyone to do as they please regarding color is that very few men have been taught the basics of color sense. Hence we end up with the "Golf outfit". 53 different colors in 32 different patterns all in the same outfit. Think of any outfit in the movie "Caddy Shack". That stuff really happens and can be see almost any day.

When in doubt, ask your wife. Then look in a mirror.